It is also implemented in dNethack as a chaotic bronze roundshield that can be enchanted to +7, and #invoking toggles conflict. (it retains the reflection and hallucination resistance)

Use

The main virtue of Mirrorbright is simply that it is a shield of reflection that neutrals can receive via sacrifice. This can provide a much-needed property early in the game and/or save a character a wish. However, it is certainly not worth an artifact wish by itself; wish for a normal shield of reflection instead. Hallucination resistance is only marginally useful in the early game, and is almost completely superseded by a well-enchanted unicorn horn.

Unfortunately, Mirrorbright actually poses something of a problem for healers. It is their first sacrifice gift; as such, it is rather unhelpful. Reflection is very useful, but in general, healers won't want to get it from a shield of reflection, as it makes spellcasting - which many healers will rely on - almost useless. Additionally, the guaranteed gift of Mirrorbright makes it far more difficult for healers to acquire an artifact weapon, which only worsens their generally low hitting power.